The present invention relates to the support of mine roofs and, in particular, to an apparatus including a roof drill bit for drilling bolt holes in mine roofs.
During a mining operation, the roof of the mine must be supported. This has traditionally been accomplished by bolting support plates to the roof after bolt-receiving holes have been drilled into the roof.
It has been conventional to drill the bolt-receiving holes by means of a drill bit comprised of a body having a plurality of cutting edges spaced apart circumferentially on a front face of the body. The cutting edges can be formed by cutting inserts made of a hard material such as cemented carbide or polycrystalline diamond for example.
The drill bit includes a rearwardly extending shank of non-circular cross-section mounted in the hollow front end of a drill bar which forms a drive shaft for the insert.
Each cutting edge communicates with a respective longitudinal channel formed along an external periphery of the body. Flushing water is directed upwardly under pressure through the drill bar and then along the channels for flushing away the cuttings and cooling the cutting edge. The water-entrained cuttings exit the hole through an annulus formed between the drill and the side wall of the hole. By flushing away the cuttings, the cutting edges stay sharper longer and the rate of drilling is increased, because the cutting edges do not have to re-cut the cuttings. Also, the cooling of the cutting edges extends their life, especially in the case of cutting edges formed of polycrystalline diamond.
Although prior art drills have functioned to flush cuttings and cool the inserts, room for improvement remains. In that regard, if the flow pattern of the cooling fluid could be improved to provide an enhanced removal of cuttings and insert cooling, it is possible that the rate of drilling could be increased, the insert life and cutting edge sharpness could be extended, and/or fewer inserts (i.e., a less expensive drill) could be used to achieve drilling rates which are comparable to presently available rates. The present invention has as its goal the attainment of some or all of those advantages.